Adds tls_edit utility which patches irt_core.nexe's TLS usage.

tests/irt_private_pthread/nacl.scons

 # -*- python -*-
 # Copyright (c) 2012 The Native Client Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 Import('env')
 
 # This test needs the IRT version of __aeabi_read_tp, and not the one that
 # gets linked into pexes post-translation.
 if env.Bit('bitcode'):
   Return()
 
 # This test reports races under tsan because:
 #  * The Valgrind interceptors are not hooked up because we are not
 #    linking this test with '-Wl,-u,have_nacl_valgrind_interceptors'.
 #  * The Valgrind interceptors don't work because we use malloc() in
 #    __pthread_initialize() and the intercepted malloc() uses TLS.
 is_broken = env.Bit('running_on_valgrind')
 
-irt_thread_test_nexe = env.ComponentProgram(
-    'irt_thread_test', ['irt_thread_test.c'],
+irt_thread_test_raw = env.ComponentProgram(
+    'irt_thread_test_raw', ['irt_thread_test.c'],
     EXTRA_LIBS=['irt_support_private'])
+
+irt_thread_test_nexe = env.ApplyTLSEdit(
+    'irt_thread_test.nexe',
+    irt_thread_test_raw)
+
 node = env.CommandSelLdrTestNacl('irt_thread_test.out', irt_thread_test_nexe)
 env.AddNodeToTestSuite(node, ['small_tests'], 'run_irt_thread_test',
                        is_broken=is_broken)